U.S. patent application number 13/512910 was filed with the patent office on 2012-09-20 for method and device for compensating frequency response of a filter unit in remote radio unit in real time.
This patent application is currently assigned to TELEFONAKTIEBOLAGET L M ERICSSON (PUBL). Invention is credited to Jack Xu.
Application Number | 20120236923 13/512910 |
Document ID | / |
Family ID | 44145073 |
Filed Date | 2012-09-20 |
United States Patent
Application |
20120236923 |
Kind Code |
A1 |
Xu; Jack |
September 20, 2012 |
Method and Device for Compensating Frequency Response of a Filter
Unit in Remote Radio Unit in Real Time
Abstract
A method for compensating frequency response of a filter unit in
remote radio unit in real time, said remote radio unit comprises
filter unit equalizer, transmitter observation receiver and antenna
calibration receiver, said method comprising the steps of:
receiving input signal of said filter unit by transmitter
observation receiver; receiving output signal of said filter unit
by antenna calibration receiver; calculating coefficients of filter
unit equalizer in real time based on said input signal and said
output signal; updating said filter unit equalizer based on said
calculated coefficients in order to compensate frequency response
of said filter unit. A device to carry out the above method, remote
radio unit comprising said device and a telecommunication system
comprising said remote radio unit are also provided.
Inventors: |
Xu; Jack; (Beijing,
CN) |
Assignee: |
TELEFONAKTIEBOLAGET L M ERICSSON
(PUBL)
Stockholm
SE
|
Family ID: |
44145073 |
Appl. No.: |
13/512910 |
Filed: |
December 9, 2009 |
PCT Filed: |
December 9, 2009 |
PCT NO: |
PCT/CN2009/001408 |
371 Date: |
May 31, 2012 |
Current U.S.
Class: |
375/232 ;
375/229 |
Current CPC
Class: |
H04B 17/12 20150115;
H03F 1/3241 20130101; H04B 2001/0425 20130101 |
Class at
Publication: |
375/232 ;
375/229 |
International
Class: |
H04L 27/01 20060101
H04L027/01 |
Claims
1.-20. (canceled)
21. A method for compensating a frequency response of a Filter Unit
(FU) in a Remote Radio Unit (RRU) in real time, the RRU comprising
a FU equalizer, a Transmitter Observation Receiver (TOR), and an
Antenna Calibration Receiver (ACR), the method comprising:
receiving an input signal of the FU by the TOR; receiving an output
signal of the FU by the ACR; calculating coefficients of the FU
equalizer in real time based on the input signal and the output
signal; updating the FU equalizer based on the calculated
coefficients in order to compensate the frequency response of the
FU.
22. The method of claim 21 further comprising loading a default
value coefficient of the FU equalizer while initializing the RRU,
prior to receiving the input signal of the FU by the TOR.
23. The method of claim 22 further comprising: Testing the RRU by a
test signal; storing the default value coefficient of the FU
equalizer in memory during the testing.
24. The method of claim 22 wherein the default value coefficient of
the FU equalizer is a coefficient of the FU equalizer used when a
FU equalizer error occurs.
25. The method of claim 21 wherein the calculating coefficients of
the FU equalizer comprises: comparing the input signal of the FU
with the output signal of the FU; extracting a frequency response
of the FU; obtaining a frequency response of the FU equalizer by
inversing the frequency response of FU; calculating coefficients of
the FU equalizer using an adaptive equalizer algorithm.
26. The method of claim 25 wherein the adaptive equalizer algorithm
is implemented by adaptive filtering.
27. The method of claim 26 wherein the adaptive filtering is one of
Least Mean Square (LMS) or an Inverse Fast Fourier Transform
(IFFT).
28. The method of claim 21 wherein the FU is a wide band passive
filter.
29. The method of claim 21 wherein the FU equalizer is implemented
as a digital filter with programmable coefficients.
30. A device for compensating a frequency response of a Filter Unit
(FU) in a Remote Radio Unit (RRU) in real time, the device
comprising: a Transmitter Observation Receiver (TOR) configured to
receive an input signal of the FU; an Antenna Calibration Receiver
(ACR) configured to receive an output signal of the FU; a
calculating unit configured to calculate coefficients of a FU
equalizer in real time based on the input signal and the output
signal; an updating unit configured to update the FU equalizer
based on the calculated coefficients in order to compensate the
frequency response of the FU.
31. The device of claim 30 further comprising a loading unit
configured to load a default value coefficient of the FU equalizer
during initialization of the RRU.
32. The device of claim 31 wherein the default value coefficient is
stored in memory during testing of the RRU by a test signal.
33. The device of claim 31 wherein the default value coefficient is
a coefficient of the FU equalizer used when a FU equalizer error
occurs.
34. The device of claim 30 wherein the calculating unit is
configured to: compare the input signal of the FU with the output
signal of the FU; extract a frequency response of the FU; obtain a
frequency response of the FU equalizer by inversing the frequency
response of the FU; calculate coefficients of the FU equalizer
using an adaptive equalizer algorithm.
35. The device of claim 34 wherein the adaptive equalizer algorithm
is implemented by adaptive filtering.
36. The device of claim 35 wherein the adaptive filtering is one of
Least Mean Square (LMS) or an Inverse Fast Fourier Transform
(IFFT).
37. The device of claim 30 wherein the FU is a wide band passive
filter.
38. The device of claim 30 wherein the FU equalizer is implemented
as a digital filter with programmable coefficients.
39. The device of claim 30 wherein the device is included in a
Remote Radio Unit (RRU).
Description
TECHNICAL FIELD
[0001] The present application generally relates to remote radio
unit, and more particularly, to a method and device for
compensating frequency response of a filter unit in real time in
such a remote radio unit.
ABBREVIATIONS
[0002] LTE long Term Evolution
[0003] RRU Remote Radio Unit
[0004] QAM Quadrature Amplitude Modulation
[0005] FU Filter Unit
[0006] EVM Error Vector Magnitude
[0007] RU Radio Unit
[0008] WCDMA Wideband Code Division Multiple Access
[0009] TOR Transmitter Observation Receiver
[0010] LMS Least Mean Square
[0011] IFFT Inverse Fast Fourier Transform
[0012] TD-SCDMA Time Division-Synchronous Code Division Multiple
Access
[0013] AC Antenna Calibration
[0014] DPD Digital Pre-Distortion
BACKGROUND
[0015] For long Term Evolution (LTE), Remote Radio Unit (RRU) must
support high order modulation signal, such as 64 Quadrature
Amplitude Modulation (QAM). If filter unit (FU) frequency response
(in both phase and amplitude) could not be compensated, EVM link
budge become too tighten. EVM characterizes modulation precision,
and is a key index of judging digital modulation quality in modern
wireless communication system. EVM is vector difference between
ideal measurement component I (In Phase) and Q (Quadrature Phase)
(referred to as reference signal "R") of transmitted signal and I,
Q component amplitude of the actually received measurement signal
"M".
[0016] In prior art, to resolve the problem, Ericsson has imported
FU equalizer to WCDMA RU and RRU product in order to improve EVM
performance. However, FU must be placed in a factory, then
characteristics of FU is to be tested and stored in a database. RRU
application software read it from said database, then calculates
the matched Finite Impulse Response (FIR) filter to inverse said
characteristics of FU, whereby compensating the FU frequency
response and improving the EVM performance. It takes a liter bit
time for production and adds a small cost.
[0017] Problems with prior art are as follows:
[0018] 1. Each FU needs external test equipment/time;
[0019] 2. External storage (or data space) is needed to store the
FU characteristics;
[0020] 3. After being delivered to operator, the change of FU,
temperature change, aging etc could no be tracked in real time;
[0021] 4. During the production, the FU could not replace without
calibration and external cost for RRU repair on production line are
added.
[0022] Consequently, there is a need for a method and a device for
compensating frequency response of FU in RRU in real time.
SUMMARY
[0023] Therefore, it is the object of the present invention to
obviate or mitigate at least some of the above limitations by
providing a method and a device for compensating frequency response
of FU in RRU in real time.
[0024] In TDD RU design, the RRU has a dedicated antenna
calibration (AC) port to support smart antenna that featured in
TD-SCDMA. In this application, by employing Antenna Calibration
(AC) and Transmitter Observation Receiver (TOR) path, real time FU
Equalizer solution is given.
[0025] In one aspect of the invention, a method for compensating
frequency response of FU in RRU in real time is provided. Said
remote radio unit comprises filter unit equalizer, transmitter
observation receiver and antenna calibration receiver, said method
comprising the steps of:
[0026] a) receiving input signal of said filter unit by transmitter
observation receiver;
[0027] b) receiving output signal of said filter unit by antenna
calibration receiver;
[0028] c) calculating coefficients of filter unit equalizer in real
time based on said input signal and said output signal;
[0029] d) updating said filter unit equalizer based on said
calculated coefficients in order to compensate frequency response
of said filter unit.
[0030] In a preferred embodiment, before step a), said method also
comprises:
[0031] e) loading a default value coefficient of FU equalizer while
initialing RRU.
[0032] In a preferred embodiment, said step of calculating
coefficients of filter unit equalizer comprises the steps of:
[0033] comparing said input signal of FU with said output signal of
FU;
[0034] extracting frequency response of FU;
[0035] obtaining frequency response of FU equalizer by inversing
said frequency response of FU;
[0036] calculating coefficients of FU equalizer by an adaptive
equalizer algorithm.
[0037] In an embodiment of the method, said adaptive equalizer
algorithm can be implemented by adaptive filtering, such as Least
Mean Square, Inverse Fast Fourier Transform and so on.
[0038] In an embodiment of the method, said default value
coefficient of FU equalizer can be stored into memory when RRU is
tested by test signal.
[0039] In an embodiment of the method, said default value
coefficient of FU equalizer can be a coefficient of FU equalizer
used at a time point when FU equalizer error occurs.
[0040] In an embodiment of the method, said filter unit is wide
band passive filter.
[0041] In an embodiment of the method, said filter unit equalizer
is implemented as digital filter with programmable
coefficients.
[0042] In another aspect of the invention, a device for
compensating frequency response of a Filter Unit (FU) in Remote
Radio Unit (RRU) in real time, said device comprises:
[0043] Transmitter Observation Receiver (TOR) for receiving input
signal of said FU;
[0044] Antenna Calibration Receiver (ACR) for receiving output
signal of said FU;
[0045] calculating unit for calculating coefficients of FU
equalizer in real time based on said input signal and said output
signal;
[0046] updating unit for updating said FU equalizer based on said
calculated coefficients in order to compensate frequency response
of said filter unit.
[0047] In an embodiment, said device also comprises:
[0048] loading unit for loading a default value coefficient of FU
equalizer while initialing RRU.
[0049] In an embodiment, said calculating unit comprises:
[0050] comparing means for comparing said input signal of FU with
said output signal of FU;
[0051] extracting means for extracting frequency response of
FU;
[0052] obtaining means for obtaining frequency response of FU
equalizer by inversing said frequency response of FU;
[0053] calculating means for calculating coefficients of FU
equalizer by an adaptive equalizer algorithm.
[0054] In an embodiment of the device, said adaptive equalizer
algorithm can be implemented by adaptive filtering, such as Least
Mean Square, Inverse Fast Fourier Transform and so on.
[0055] In an embodiment of the device, said default value
coefficient of FU equalizer can be stored into memory when RRU is
tested by test signal.
[0056] In an embodiment of the device, said default value
coefficient of FU equalizer can be a coefficient of FU equalizer
used at a time point when FU equalizer error occurs.
[0057] In an embodiment of the device, said filter unit is wide
band passive filter.
[0058] In an embodiment of the device, said filter unit equalizer
is implemented as digital filter with programmable
coefficients.
[0059] In yet another aspect of the invention, a RRU comprising the
device according to the invention is provided.
[0060] In yet another aspect of the invention, a telecommunication
system comprising the RRU according to the invention is
provided.
[0061] Advantages of the present invention comprise: the FU
characteristic is calculated on application environment; since no
hardware changes between normal operation and calibration phase,
best performance can be obtained in real time; the equalization can
be done on demand; it can track any change of FU on application
environment; the FU replacement cost can be reduced and FU can be
replaced without recalibration.
BRIEF DESCRIPTION OF THE DRAWINGS
[0062] The invention, together with further objects and advantages
thereof, may be understood by making reference to the following
description taken together with the accompanying drawings, in
which:
[0063] FIG. 1 is a schematic block diagram of RRU in which the
present invention can be implemented;
[0064] FIG. 2 is a schematic flow diagram of an embodiment of a
method for compensating frequency response of a filter unit in
remote radio unit in real time according to the present
invention;
[0065] FIG. 3 is a schematic flow diagram of a preferred embodiment
of the inventive method;
[0066] FIG. 4 is a schematic flow diagram of a preferred embodiment
of step s203 illustrated in FIG. 2;
[0067] FIG. 5 is a schematic block diagram of an embodiment of a
device for compensating frequency response of a filter unit in
remote radio unit in real time according to the present
invention;
[0068] FIG. 6 is a schematic block diagram of a preferred
embodiment of a device for compensating frequency response of a
filter unit in remote radio unit in real time according to the
present invention;
[0069] FIG. 7 is a schematic block diagram of an embodiment of
calculating unit comprised in said device shown in FIG. 5 according
to the present invention.
[0070] Corresponding reference characters indicate corresponding
components throughout the several views of the drawings.
DETAILED DESCRIPTION
[0071] The embodiments set forth below represent the necessary
information to enable those skilled in the art to practice the
invention and illustrate the best mode of the practicing the
invention. Upon reading the following description in light of the
accompanying drawing figures, those skilled in the art will
understand the concepts of the invention and will recognize
applications of these concepts not particularly addressed herein.
It should be understood that these concepts and applications fall
within the scope of the disclosure and the accompanying claims.
[0072] A brief description of the different parts of the RRU in
FIG. 1 is given below.
[0073] RRU comprises Power Amplifier (PA) 1, Filter Unit (FU) 2,
Transmitter Observation Receiver (TOR) 3, Antenna Calibration (AC)
receiver 4, FU equalizer 5 and real time equalizer 6. Of course,
RRU also comprises other known components, which are unnecessary to
understand the invention so that said components are not discussed
therein. Further, PA 1 is a prefer component for amplifying the
input signal. Therefore, without PA 1, the present invention can be
achieved.
[0074] Preferably, FU 2 is wide band passive filter in TDD RRU
system, the transmitter and receiver share the same FU by different
time slot, that is, in TDD system, the AC will share the hardware
of receiver, and in transmitter time, the receiver is free for AC.
AC port can receive the transmitter signal from the AC (without
FU). FU equalizer 5 can be implemented by digital filter with
programmable coefficients and different FU use a different set of
coefficients.
[0075] During manufactory test, test signal is sent to power
amplifier 1 and then is received by TOR 3 and FU 2. Said signal is
filtered by FU 2 and then is transmitted to AC receiver 4 by air
interface. Real time equalizer 6 will compare the TOR signal with
AC receiver signal. The FU characteristics can be extracted by real
time equalizer 6. The FU equalizer characteristics are obtained by
inversing the FU characteristics. It is easy to calculate the
coefficients of FU equalizer by adaptive filtering, such as LMS
(Least Mean Square), IFFT (Inverse Fast Fourier Transform) and so
on. In doing so, a default value coefficient of filter unit
equalizer can be obtained. Of course, test signal is generated by
test signal generator in RRU. Then, said default value coefficient
of filter unit equalizer can be stored in memory, such as flash
memory.
[0076] In another option, said default value coefficient of FU
equalizer can be a coefficient of FU equalizer used at a time point
when FU equalizer error occurs.
[0077] Preferably, when normal traffic is transmitted, in order to
speed up the filter going to a stable condition, the FU equalizer 5
will load said default value coefficient from real time equalizer
6. These coefficients will be defined as the start value
coefficients of filter unit equalizer. During RRU working,
frequency response of FU 2 will be tracked in real time. The
adaptive equalizer algorithm will modify the coefficients by
checking input signal of FU (that is TOR data) and output data of
FU (that is AC data). Then the FU distortion can be
compensated.
[0078] With reference to FIG. 2, an embodiment of a method for
compensating frequency response of a FU 2 in remote radio unit in
real time according to the present invention will be described.
[0079] At step s201, transmitter observation receiver receives
input signal of said filter unit 2. After input signal is filtered
by FU 2, antenna calibration receiver receives output signal of
said filter unit at step s202. Then at step s203, coefficients of
filter unit equalizer are calculated by real time equalizer based
on said input signal and said output signal. Finally, at step s204,
said filter unit equalizer 5 is updated based on said calculated
coefficients in order to compensate frequency response of said
filter unit 2.
[0080] In a preferred embodiment of the invention, refer to FIG. 3,
said method first performs the step of:
[0081] loading a default value coefficient of FU equalizer while
initialing RRU, s301.
[0082] Then said method performs steps s302-s305, which are the
same as steps s201-s204 in FIG. 2, so these steps are not described
in detailed.
[0083] As stated above, when RRU goes to initialization status, in
order to speed up the filter going to a stable condition and
shorten convergence process, FU equalizer will load a default value
coefficient of FU equalizer. How to obtain said default value
coefficient has the following two options:
[0084] One option is done in the process of manufacturing, which is
optional and not essential. During manufactory test, under
application software and firmware control, test signal is
generated. The test signal can be a Multi Tone signal that occupies
the whole bandwidth of normal operation. After amplified by PA 1,
the test signal was received by TOR 3, then the input signal of FU
2 is known by real time equalizer. The test signal is filter by FU
2, it makes some distortion on amplitude and phase. The calibration
antenna will pick up this filtered signal and then this filtered
signal is sent to AC receiver 4. The real time equalizer 6 will
compare the TOR signal with AC receiver signal. The FU
characteristics can be extracted by the real time equalizer 6 and
the frequency response of FU equalizer can be obtained by inversing
the FU frequency response. It is easy to calculate the coefficients
of FU equalizer by adaptive filtering, such as LMS, IFFT and so on.
From this, we can obtain default value coefficient of FU equalizer.
Of course, the test signal can be generated by test signal
generator in RRU, then test signal performs the above actions,
finally default value coefficient of FU equalizer can be
obtained.
[0085] Another option is that default value coefficient of FU
equalizer comes from the normal operation when the error of
Equalizer reaches a certain threshold.
[0086] In summary, obtaining a default value coefficient of FU
equalizer is a preferred embodiment. The technical effect in doing
so is to speed up the process and shorten convergence time.
[0087] In a preferred embodiment of the invention, refer to FIG. 4,
said step s203 of calculating coefficients of FU equalizer
comprises the steps of:
[0088] comparing said input signal of FU with said output signal of
FU, s401,
[0089] extracting frequency response of FU, s402;
[0090] obtaining frequency response of FU equalizer by inversing
said frequency response of FU, s403;
[0091] calculating coefficients of FU equalizer by an adaptive
equalizer algorithm, s404.
[0092] In a preferred embodiment, said adaptive equalizer algorithm
can be implemented by adaptive filtering, such as Least Mean
Square, Inverse Fast Fourier Transform and so on.
[0093] Refer to FIG. 5, FIG. 5 is a schematic block diagram of an
embodiment of a device for compensating frequency response of a
filter unit in remote radio unit in real time according to the
present invention. Said device is used to implement the above
described method according to the invention. Said device comprises
TOR 3 for receiving input signal of said filter unit, AC receiver 4
for receiving output signal of said filter unit, calculating unit
501 for calculating coefficients of filter unit equalizer in real
time based on said input signal and said output signal, updating
unit 502 for updating said filter unit equalizer based on said
calculated coefficients in order to compensate frequency response
of said filter unit. Said calculating unit 501 and said updating
unit 502 can be implemented in real time equalizer 6.
[0094] In a preferred embodiment, said device also comprises
loading unit for loading a default value coefficient of FU
equalizer while initialing RRU. Said default value coefficient of
FU equalizer can be stored into memory when RRU is tested by test
signal, or said default value coefficient of FU equalizer comes
from the normal operation when the error of equalizer reaches a
threshold. Loading unit is introduced in order to speed up the
process and shorten convergence time.
[0095] Further, refer to FIG. 6, FIG. 6 is a schematic block
diagram of a preferred embodiment of a device for compensating
frequency response of a filter unit in remote radio unit in real
time according to the present invention. In order to speed up the
progress and shorten convergence time, said device also comprises
loading unit 601 for loading a default value coefficient of FU
equalizer while initialing RRU. In a preferred embodiment, when
normal traffic is transmitted, loading unit 601 first loads a
default value coefficient of FU equalizer, then calculating unit
501 calculates coefficients of filter unit equalizer, finally
updating unit 502 updates said FU equalizer. Said loading unit 601
can also be implemented in real time equalizer 6.
[0096] In another preferred embodiment, refer to FIG. 7,
calculating unit 501 comprises:
[0097] comparing means 701 for comparing said input signal of FU
with said output signal of FU;
[0098] extracting means 702 for extracting frequency response of
FU;
[0099] obtaining means 703 for obtaining frequency response of FU
equalizer by inversing said frequency response of FU;
[0100] calculating means 704 for calculating coefficients of FU
equalizer by an adaptive equalizer algorithm.
[0101] In a preferred embodiment, said adaptive equalizer algorithm
can be implemented by adaptive filtering, such as Least Mean
Square, Inverse Fast Fourier Transform and so on.
[0102] Calculating unit 501, configuring unit 502 and loading unit
601 may be implemented in hardware, firmware, software or any
combination thereof.
[0103] Advantages of the present invention comprise: the FU
characteristic is calculated on application environment; since no
hardware changes between normal operation and calibration phase,
best performance can be obtained real time; the equalization can be
done on demand; it can track any change of FU on application
environment; the FU replacement cost can be reduced and FU can be
replaced without recalibration.
[0104] Throughout the description and claims of this specification,
the words "comprise", "include" and "contain" and variations of the
words, for example "comprising" and "comprises", means "including
but not limited to", and is not intended to (and does not) exclude
other components, integers or steps.
[0105] Throughout the description and claims of this specification,
the singular encompasses the plural unless the context otherwise
requires. In particular, where the indefinite article is used, the
specification is to be understood as contemplating plurality as
well as singularity, unless the context requires otherwise.
[0106] It will be understood that the foregoing description of the
embodiments of the invention has been presented for purposes of
illustration and description. This description is not exhaustive
and does not limit the claimed invention to the precise forms
disclosed. Modifications and variations are possible in light of
the above description or may be acquired from practicing the
invention. The claims and their equivalents define the scope of the
invention.
* * * * *